The present invention relates to a method and/or architecture for implementing an oscillator generally and, more particularly, to a method and/or architecture for implementing a digitally compensated voltage controlled oscillator.
Conventional approaches for implementing voltage controlled oscillators include tuning capacitors implemented as (i) varactor diodes and (ii) various forms of voltage controlled capacitance circuits. VCOs implementing such approaches are difficult to build with a typical CMOS fabrication process and have poor linear transfer characteristics.
Conventional approaches for implementing digital controlled oscillators include (i) EPROM table capacitance equivalence for a crystal oscillator/PLL circuit and (ii) digitally controlled capacitance without fine tuning capabilities. None of these conventional approaches compensates for non-linear capacitance effects.
The present invention concerns an apparatus comprising a digitally controlled oscillator and a frequency tuning array. The digitally controlled oscillator may be configured to finely tune an output signal having a frequency in response to a digital signal. The frequency tuning array may be configured to generate the digital signal.
The objects, features and advantages of the present invention include providing a method and/or architecture for implementing a digitally compensated voltage controlled oscillator that may (i) receive a user voltage level, (ii) implement a voltage controlled oscillator (VCO) using a frequency tuning array to fine tune a particular frequency, (iii) provide automatic fine tuning, (iv) implement a capacitance controlled crystal oscillator to operate as a fine tuned digitally controlled oscillator, (v) provide a number of tuning operation modes, (vi) allow each of the operation modes to operate independently, (vii) determined a particular mode in response to a capacitance, and/or (viii) set an oscillator capacitance in response to the mode of operation by (a) an analog voltage signal, (b) a digital signal comprising a first digital word from a control register, and (c) a digital signal comprising a second digital word to a frequency tuning array.